Answer: Blue nevus and meningioma

Histology: Within the dermis there is a typical blue nevus. Deeper down within the dermis and subcutaneous fat most of the lesion has the appearance of anastomosing channels. Bundles of collagen separate the channels and are lined by cytologically bland cells. There is no blood or eosinophilic secretions within these spaces. This process extends around skin adnexal structures and focally there are areas of increased cellularity consisting of small nests of cells containing ovoid nuclei.

Discussion: This lesion is typical of what has been reported previously as “hamartoma of the scalp with ectopic meningothelial elements.” This lesion was reported by Saul Suster and Juan Rosai in 1990 (Am J Surg Pathol 14:1-11,1990.). As in the current case, lesions present in the scalp and were seen in patients ranging from 4 months to 40 years of age. These lesions mimic angiosarcoma as in the current case. In contrast to angiosarcoma, there is no cytologic atypia in the cells lining the spaces. Furthermore, one would expect to see red blood cells in some of the channels which was absent from the current case. The current case and those previously reported were negative for vascular markers and were strongly positive for EMA consistent with meningioma. Focally in the current case the lesion reveals its typical meningothelial nature with nests of cells with ovoid nuclei. Suster and Rosai considered these lesions to be more hamartomatous rather than ectopic meningothelial in nature. In the current case, although it was considered unlikely, clinicians were notified to evaluate the possibility of a meningioma extending through the calvarium into the underlying subcutaneous tissue. On subsequent imaging studies, there was no evidence of a dural based meningioma. It is unclear what the relationship of the blue nevus is to the meningothelial lesion.